- Two ethnic groups inhabit the Negev region of Israel, Beduins and Jews. They differ in their birth-rate, life style and nutritional and growth patterns. We report an epidemiological study of acute RVD among <3 yr olds in 2 small urban communities a) Bedouin with 700 births/yr b) Jewish with 500 births/yr. 296 Bedouins (212 with diarrhoea & 84 controls) and 215 Jews (135 with diarrhoea & 80 controls) were enrolled. 60% with diarrhoea and all controls were studied as outpatients. Median age was 10m in both groups. RVD was detected in 64/444 (14%) with diarrhoea against 3/163 (2%) of controls (p<0.001). RVD was more common than C jejuni (9%), Shigella (4%), Salmonella (3%), E.P.E.C. (8%) G. lamblia (8%) and Cryptosporidium (5%). No differences in relative frequency of diarrhoea were found between hospitalized and non-hospitalized, Jews and Bedouins or well and mal-nourished patients. The percentage of RVD was highest during winter (30%) (p<0.01). We estimated that 2% of the Bedouins, but only 0.2% of the Jews with RVD during their first year of life were hospitalized. Vomiting was more frequent among patients with RVD (43/57)-75%) than among patients with other causes of diarrhoea (194/360-54%) (p<0.005). No differences were observed in other clinical variables or stool appearances between patients with or without RVD. RVD is a leading cause of morbidity of young children in our community. Efforts should be concentrated on appropriate immunization.